Changing content of \multicolumn causes a LaTeX error

[jtappin]

In a table containing a number of \multicolumn items in the header, completely changing the content of one results in an output file that reports a LaTeX error.

Original file:

  \begin{tabular}{lrrrrrrrr}
    \hline
    Instrument & $\lambda$ (nm) & $\log_2 N_{\mathrm{G}}$ &
    \multicolumn{2}{c}{Width (mm)}& \multicolumn{2}{c}{Pitch (\micron)}
    & \multicolumn{2}{c}{Ratio to Disk}\\
               & & & Min & Max & Min & Max & Min & Max\\
    \hline

Updated file:

  \begin{tabular}{lrrrrrrrr}
    \hline
    Instrument & $\lambda$ (nm) & $\log_2 N_{\mathrm{G}}$ &
    \multicolumn{2}{c}{Width (mm)}& \multicolumn{2}{c}{Pitch (\micron)}
    & \multicolumn{2}{c}{Grid margin}\\
               & & & Min & Max & Min & Max & Min & Max\\
    \hline

latexdiff output:

  \begin{tabular}{lrrrrrrrr}
    \hline
    Instrument & $\lambda$ (nm) & $\log_2 N_{\mathrm{G}}$ &
    \multicolumn{2}{c}{Width (mm)}& \multicolumn{2}{c}{Pitch (\micron)}
    & \DIFdelbeginFL %DIFDELCMD < \multicolumn{2}{c}{Ratio to Disk}%%%
\DIFdelendFL \DIFaddbeginFL \multicolumn{2}{c}{Grid margin}\DIFaddendFL \\
               & & & Min & Max & Min & Max & Min & Max\\
    \hline

pdflatex error:

! Misplaced \omit.
\multispan ->\omit 
                   \@multispan 
l.714 ...ddbeginFL \multicolumn{2}{c}{Grid margin}
                                                  \DIFaddendFL \\
? 

If I press return at the prompt, the resultant PDF file shows the new version only with no highlighting.

Running on Manjaro Linux with:

$ latexdiff --version
This is LATEXDIFF 1.3.3 (Algorithm::Diff 1.15 so, Perl v5.38.0)
  (c) 2004-2022 F J Tilmann

[norbertroamsys]

We have encountered this issue/bug too. Are there any plans to fix it in the future?

[ftilmann]

I just tested the example above. I cannot fully reproduce this, as for me it just compiles without an error but also the change is invisible. You (@jtappin) did not post a full MWE but just a snippet, and the context might have made the difference (e.g. \micron did not work for me and I had to replace with $\mu$. The problem with visibility is easy to fix. I just tried with latexdiff --append-textcmd=multicolumn and at least for the example it works. Most likely, this will be default from (future) 1.3.4 onwards but I need to do some testing first.

[ftilmann]

As show, this is now implemented. Hopefully it also fixes your problems although I never managed to reproduce them.